The broad objective of this investigation is to obtain electrophysiological and neuropharmacological data concerning synaptic mechanism and neuronal responsiveness to putative neurotransmitters of basal ganglia neuronal systems, the globuspallidus and its afferent and efferent systems, in particular. The responsiveness of primate globus pallidus neurons to microiontophoretically applied putative inhibitory neurotransmitters lambda-aminobutyric acid (GABA), glycine, taurine and beta-alanine was studied. Macaca mulatta monkeys anesthetized with chloralose-urethane were used as the experimental animal. One hundred forty two pallidal neurons were studied; of these 101 were located in the internal segment, 30 in the external segment and 11 in the transition area. Both dose-response and time-response curves have been employed to compare the depressant effects of these four inhibitory amino acids before, during and after the microiontophoretic administration of strychnine or picrotoxin. The ED-50 dose, in terms of nanoamps of current required to produce 50% depression of spontaneous neuronal firing, was 13.5, 29, 56, 86 for GABA, glycine, beta-alanine and taurine, respectively. Strychnine antagonized the depressant effects of glycine, taurine and beta-alanine, whereas picrotoxin antagonized the depressant effects of GABA. Stimulation studies have demonstrated that the striopallidal pathway in monkey is inhibitory to some pallidal neurons. Stimulation of the caudate nucleus resulted in inhibition of spontaneous firing of globus pallidus neurons; the duration of this inhibition was greater than 200 msec. Studies are now underway to try to pharmacologically characterize this inhibition employing GABA and glycine antagonists. Our electrophysiological studies on the pallidothalamic system indicate that this system is inhibitory to neurons located in the ventral most region of ventralis lateralis oralis and ventralis lateralis medialis. Studies are now underway to determine if afferent projections from the cerebellum (dentatothalamic), the globus pallidus (pallidothalamic substantia nigra (nigrothalamic) and the motor cortex (corticothalamic) converge onto single ventral leteral and/or ventral anteriorthalamic neurons.